Level marking for telephone line finders



y 1951 c. F. FFOLLIOTT 2,552,773

LEVEL MARKING FOR TELEPHONE LINE FINDERS Filed June 24, 1947 2 Sheets-Sheet 1 INVENTOR.

CHARLES F. FFOLLIOTT ATTORNEY May 15, 1951 c. F. FFOLLIOTT LEVEL MARKING FOR TELEPHONE LINE FINDERS Filed June 24, 1947 2 Sheets-Sheet 2 m w 7 m 2 5 3 2 9 a a L m a m a 2 R E w o L L A 0 T e 3 0 2 5 I INVENTOR. GHARLES F. FFOLLIOTT ATTORNEY f Patented May 15, 1951 LEVEL MARKING FOR TELEPHONE LINE FIND ERS

Charles F. Ffolliott, Elgin, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application June 24, 1947, Serial No. 756,573

'7 Claims.

The present invention relates in general to automatic telephone systems, and more particularly to systems in which linefinders connect a subscribers calling line to a first numerical switch.

Anobjectof the invention is to provide control circuits to allow efficient simultaneous operation of a plurality of finders employing standard Stro-wger switches.

One feature relates to level-marking cut-off relays which remove the marking potential from the vertical bank contacts.

Another feature of the invention permits only one line relay of one level or of associated levels to operate at one time.

Figures 1 and 2 arranged together show subscribers line equipment, finders, allotters, and associated start and control means. The line circuit of Figure 3 showing one 2-step relay may be substituted for that in Figure 1 showing separate line and cut-off relays.

In Figure 2, the 200-line finder at the left, and the allotter at the right are in general similar to those disclosed in Patent 1,851,132, issued March 29, 1932, to Norman H. Saunders. Formerly, the finders were divided into two groups and each group had one allotter; but in the present illustration all finders of a 200- line system are in one group and are equally accessible by three allotters. The finder switch includes wipers 20I to 296 inclusive, vertical stepping magnet 21,6, rotary stepping magnet 21-1, and release magnet 218. The distributor is a rotary switch with stepping magnet 262, and wipers 264 to 269, inclusive.

In Figure l, the level start relays I49 to I44 correspond to relays SA, SB, SC, SD, and SE in Figure 1 of Patent 1,914,540, issued June 20,

1 933, to R. Taylor et al. In the finder system disclosed by Taylor et al. and in the finder system of the present invention the ZOO-lines are divided into five groups, each group containing two levels of forty lines which are served by a single level start relay having separate winding for each level. In addition to the ,contacts forstarting the allotters, each of the level start relays MI to 44 inclusive of the present invention controls break contacts for the op.- erating circuits of the line relays associated with the level start relay.

The levels are also associated according to their priority in starting allotters. Duringlight calling traific, any line relay of the lower four levels upon operating energizes either level start relay I43 .or 144 to place ground on al.-

2 lotter start lead I50, any "line relay of the fifth and sixth levels upon operating energizes level start relay I42 to place ground on allotter start I52, and any line of the upper four levels upon operating energizes either level start relay I40 or M] to place ground on lead I5I which starts still a different allotter. However, when the calling traffic is heavy on the lower four levels and light on the other levels, both level start relays I43 and I44 are operated simultaneously to place ground on lead I and also on allotter start lead I52 which is generally associated with the fifth and sixth levels. Moreover, possible combinations of operated start relays due to simultaneous calls within the groups enable any line to start any allotter.

Break contacts of the line relays in a group are connected in series to form a chain circuit to ground. When subscribers whose lines are connected to one group of line relays initiate calls simultaneously, only one line relay operates immediately, because the operation of the line relay with a preferred position in the chain circuit removes ground potential from the line relays connected still further from ground.

The level marking cut-01f relays It!) to 13-3 inclusive in Figure 1 permit eflicient simultaneous operation of standard Strowger finder switches. The vertical bank contact for every level except the upper two is connected to the marking ground potential through a winding of a level marking cut-off relay.

To aid in the understanding of the novel features of the invention, a general description is now given.

The operation of a line relay IIII closes its locking circuit, completes a circuit to operate a level start relay I44, and through a winding of a level marking cut-off relay I 33 places ground potential on a vertical bank contact. Upon operating, the level start relay opens the operating circuits of all the line relays of the group, and places ground on an allotter start lead. Assuming the allotter has preselected an idle finder, the wipers are stepped up to the marked vertical bank contact to complete a circuit from ground, contacts II4, level marking cut-off relay I33, vertical bank contact I95, vertical wiper I 06, distributor wiper 254, contacts 235, lower winding of changeover relay23ll, make contacts 224 to negative battery. The level marking cut-off relay operates, completes its locking circuit from ground at contacts I14 to negative battery at contacts I34, and opens the circuits to the vertical bank contacts of the two associated levels 3 in which the calling line appears. Before ground is removed from the marked vertical bank contact, the changeover relay 230 operates to close its locking circuit to its upper winding.

While the level marking cut-ofi relay at the level is operated, the wipers of another finder may 7 step on to a higher marked level.

until either the upper or lower-test wiper encounters negative battery from the calling subscribers cut-off relay. Assuming the calling line is in the upper IOU-line bank, relay 29!] operates to connect the calling line to a first numerical switch, and to return ground on the control lead. Cut-off relay 12!! operates to disconnect line relay IID from the negative line and to re- 7 move ground from the positive line.

Upon releasing, the line relay opens the circuit of the level start relay and the level marking cut-off relay simultaneously. Other line relays cf the group cannot operate to close the circuit tothe level marking cut-ofi relay until the level start relay releases. During the interval that the line relays are not operated, the level marking cut-oil relay releases to open another point in its locking circuit and to prepare the level marking circuits for the succeeding call.

A detailed description is now given. When the subscriber IiII initiates a call, the circuit for line relay H3 is completed from ground, chain contacts H2, contacts I2I of cut-off relay I20, contacts" I45 of level start relay I4 3, line 32, subscribers telephone IDI, line I93, contacts I22, winding of relay III! to negative cattery. The operation of relay IIll opens the chain at contacts H2 to prevent the operation of line relays v that are in that part of the chain further from ground. At contacts III a circuit is closed in multiple with contacts I35; at contacts H3 negative potential is extended from cut-off relay I23 to mark contact 201 in the bank of the finder; at contacts Il i ground is applied through the level-marking cut-off relay I33 to mark vertical bank contact I65; and also at contacts M3 the circuit is completed to operate level start relay I.

Relay I4 4 at contacts 35 and at other contacts such as contacts Hi8 opens the operating circuits of all line relays in the group, at contacts I46 closes the circuit of relay 2N, and at contacts I4? prepares another allotter start circuit for calls that may originate in levels three and four. Relay 2m operates. At contacts 2| I, circuits of the pulse machine 253 and of the start The wipers rotate 4 to relay 2 I5. When relay 240 operates, the armature closes the make contacts 2 M and 252 and also strikes the weighted spring 254 to start it vibrating. Relay 2&0 at contacts 2 places a multiple ground on the winding of relay 223, at contacts 252 prepares the pulsing circuit for the stepping magnets of the finder, and at contacts 243 closes the intermittent circuit including contacts 2351 and the lower winding of the slow-operating relay )0.

' Finder start relay 27E! operates. At armature 2'II ground is removed from the lead to the release magnet and is placed on control lead C; at contacts 272 the biasing circuits of relays 23c and 233 are completed; at armature 2'53 the guard lead istransferred from the vertical off-normal springs VON to cam springs 2?.2; at contacts 216 the pulsing circuit is completed for the vertical stepping magnet; and at contacts 275 the pulsing signal 2M are completed; at contacts 252 the operating circuit of relay 223 is completed from ground, contacts 252, contacts 23L contacts 2I2, winding of relay 223, interrupter contact 233,

winding of stepping magnet 282 to negative bat tery. Relay 220 at contacts 22I completes the 225 closes the circuit of relay 2%, and at contacts 75 226 prepares a circuit for a relay corresponding circuit is prepared for the rotary stepping magnet. The operating circuit of the vertical magnet maybe traced from the pulsing machine 2I3, contacts 253, contacts 232, armature 233, wiper 231, contacts 2%, vertical magnet 2% to the negative battery.

Responsive to the first step the vertical offnormal springs VON are operated; at contacts 254 the circuit for the release magnet is prepared; and at contacts 255 a circuit to ground is prepared for guarding purposes. When the vertical wiper encounters themarked contactfor example, contact I05 marking the first level-the circuit to energize relays 23c and I33 in series is closed from ground, contacts H4, lower winding of relay I33, vertical contact I05, vertical wiper I E33, wiper 234, contacts 235, lower winding of changeover relay 2%, contacts 224, to negative battery. Relay 233 operates sufficiently to. close contacts 232 which complete the circuit from ground, contacts 24 I, contacts 232, upper winding of relay230 to negative battery. Relay I33 operates, at contacts I34 closes its locking circuit and at contacts I35 removes the marking potential from the vertical bank contact I85, changeover relay 23E! operates fully through its upper winding.- At contacts 23I the initial operating ground is disconnected from relay 223; at armature 233 the pulsing circuit is transferred from the vertical stepping magnet to the rotary stepping magnet;

and at contacts 235 the test lead 233 is disconnected from the lower winding of relay 233.

Normally the circuit including the lower winding of trouble relay 25s is opened at contacts 234 before the vibrating spring 244 closes the circuit for intervals sufficiently long to operate relay 253. During the remaining time that the allotter is at this finder, the upper winding of relay 250 is closed intermittently by vibrating spring 245 and contacts 26L These, contacts are actuated by relay 260 which is energized over an obvious circuit when relay 230 is operated. V V

The operatin circuit for the rotary stepping magnet includes the pulse machine 2 I3, contacts 253, contacts 22, make contacts at armature 233, wiper 268, contacts 215, contacts 285, rotary mag- .net 211, and negative battery. When the rotary 235, bankcontact 231, contacts H3, cut-ofi relay I20 to negative battery. Relay 2% at contacts 29 I and 292 switches the calling linethrou gh to the first numerical switch, at contacts 233 completes its locking circuit to control lead C, at contacts 294- extends ground from the control lead to lead CN, at contacts 295 opens the operating circuit to relay 289, at armature 296 transfers the ground pulses from the rotary stepping magnet to the guard lead, and at contacts 291 opens a point in the incomplete circuit of the release magnet. The first numerical switch returns dial tone to the subscribers line, and places a holding ground on the control lead C.

When the switching relay places ground on lead CN, cut-off relay I29 operates, at contacts I22 disconnects line relay H9, at contacts IZI removes ground from the line, and at contacts I23 closes its locking circuit. Upon releasing relay H9 at contacts I II opens a further point in its locking circuit, at contacts I I2 prepares the operating circuit for the line relays further along in the chain, at contacts H3 opens one of the multiple circuits in the control lead, and at contacts H4 removes the ground potential from lead H5 to release relays I44 and I33.

After the release of relay H9, the operating circuits of all line relays associated with the two lower levels remain open momentarily at the break contacts of relay I44. This interval during which ground cannot be placed on lead H5 is provided to insure the release of relay I33.

Upon releasing, relay I33 prep-ares the marking circuits to the lower two levels at contacts I35 and I36, and opens a further point in its locking circuit at contacts I34. Relay I44 releases, at contacts I45 and I48 prepares the operating circuits of all line relays in the group, at contacts I46 opens the circuit to relay 2 I 9, and at contacts I41 opens the start circuit that was prepared for a call in levels three and four. Relay 2 I9 may release, or during heavy calling traffic it could remain energized by the operation of other level start relays.

Since the finder is a ZOO-point finder, and, therefore, has two sets of wipers it may so happen that test wiper 295 instead of test wiper 253 may encounter the negative battery calling potential of the calling line. In this case, the finder is operated in the same manner as previously described and when wiper 299 encounters the negative battery calling potential on the test contact associated with the calling line, a circuit will be completed for operating the switching relay 299 as follows: ground, make contacts 21I, upper winding of switching relay 299, contacts 295, and negative potential at wiper 299. Upon energizing, relay 299 at armatures 29I and 282 connects the lower set of wipers for use, at contacts 283 closes its locking circuit, at armature 294 connects the grounded release trunk conductor to the test contact of the calling line for guarding purposes, and at armature 295 opens the circuit of the rotary magnet and also places ground upon guard lead 221 to step the allotter to the next finder.

In case the test wipers 295 and 299 should simultaneously encounter calling potentials both switching relays operate, but switching relay 299 will be ineffective because the switching relay 289 disconnects the upper set of wipers, and opens the locking circuit of relay 299.

In case either of the test wipers 295 or 296 should encounter booster battery metering potential during their rotation before the calling line is reached, the booster battery would close a circuit through the upper winding of the switching relay but this circuit would be in opposition to the circuit through the polarizing winding with the result that the switching relay would not be operated.

Returning to the allotter at the time switching relay 299 operates to transfer ground pulses to guard lead 221. The circuit to energize stepping magnet 292 and to short circuit the winding of relay 229 extends from the pulse machine 2I3 to contacts 253, contacts 242, make contacts 233, wiper 298, contacts 215, break contacts 285,

make contacts 29?, make contacts 2'53, busy key, wiper 299, make contacts 222, to the stepping magnet 292, and also through interrupter springs 293 to relay 229. The magnet 262 Withdraws the pawl of the switch from the ratchet wheel and operates interrupter springs 263 opening the circuit to relay 229.

Upon releasing relay 229 at contacts 22I opens the circuit of slow-acting relay 219, at armature 222 opens the energizing circuit of magnet 262 by transferring the guard lead to the interrupter springs 293, at contacts 223 opens the ground circuit of relay 229, at contacts 224 opens a further point in the vertical test circuit, at contacts 225 opens the circuit of relay 249, and at contacts 229 prepares the circuit for relay 2 I5. Stepping magnet 292 deenergizes to advance wipers 264 to 269 inclusive to the contacts associated with another finder. Relay 249 releases, at contacts 243 opens a further point in the circuit to the lower winding of relay 259, at contacts 242 opens the ground pulse circuit, and at contacts 241 opens the circuit of relays 239 and 269. Upon releasing relay 239 at contacts 23l prepares the operating circuit of relay 229, at contacts 232 opens its locking circuit, at armature 233 transfers the incomplete pulse circuit to the vertical magnet, and at contacts 234 prepares a circuit to relay 259. Relay 269 releases to open the intermittent circuit to slow-acting relay 259 which has not operated. Relay 219 releases. At armature 21! ground is transferred from the control lead C, which is now maintained at ground potential by the holding relay of the first numerical switch, to the incomplete circuit of the release magnet. t contacts 213, ground at the vertical cit-normal springs VON is placed on a contact of the rotary switch bank for guarding purposes; at contacts 213 the circuits of the polarizing windings of relays 289 and 299 are opened; and at contacts 214 and 215 further points are opened in the pulsing circuits of the vertical magnet and the rotary magnet.

Should the wipers of the distributor advance to contacts corresponding to a busy finder, a circuit is completed from ground, contacts 255 of off-normal normal springs VON, break contacts 213, busy key, wiper 266, break contact 222, interrupter springs 253, winding of stepping magnet 262, to negative battery. The stepping magnet operates like a buzzer as long as ground potential is encountered on the guard lead. When the ground is not encountered, the wipers ,of the distributor come to rest in a position that pre-selects an. idle finder for the next call that uses this allotter.

In order that two allotters that have selected one finder do not operate simultaneously a relay 2I5 has been provided in each allotter. Conductor 288 is connected to similar contacts which correspond to the same finder in other allotters. When relay 229 operates, wiper 269 is transferred at armature 229 from the winding of relay 2I5 to ground. Another allotter having selected the same finder remains unoperated, for

the circuit toits start relay 210 is opened at armature 2H5 by its relay 215. The circuit to operate relay 215 extends from ground in theoperated allotter, make contact 226, wiper 289, conductor 288, conductor 238 in the other allotter, Wiper 269, break contact 226, winding of relay 2 l 5, to negative battery.

Although two allotters having selected the same finder advance their wipers simultaneously, they soon encounter different finders. The connections between the finders and the distributors are in an order that does not permit two distributors to select finders in the same sequence. After the conversation and responsive to the calling subscriber replacing the receiver, ground is. removed from the holding conductor C in the well known manner. Relay 2921 releases and at contacts 29? completes the circuit to release magnct'zlt. The circuit may be traced from ground, break contacts 2H, busy key, contacts 254, contacts 251i, winding of release magnet,.to negative battery. The release magnet operates and returns the wipers of the finder to their normal position. The vertical off-normal springs VON open the circuit of the release magnet and remove the ground from contact 289 to make the finder selectable.

When ground is removed from the holding conductor, cut-off relay i129 releases, and prepares the line circuits for the next call.

In case of trouble when the finder does not step or does not complete its switching operation, relay 250 operates to advance the wipers of the distributor. If the trouble is encountered before changeover relay 23f? operates to open the circuit at contacts 233, relay 256 is energized through its lower winding. As the amplitude of vibration decreases, the weighted. spring closes the circuit for longer intervals to operate slow-operating relay 25% which at contacts. 253 opens the pulsing circuit to the vertical magnet, at contacts 252 opens the initial operating circuit of relay 22d, and at contacts 25! places Contacts 345, that correspond to contactsv 14501 Figure 1, are controlled by relay IE4; and contacts 3| 2 and 396 are controlled by another line relay which is similar to relay 3H3. These line circuits are also arranged in groups, the circuits of each group being connected to two particular levels in the banks of each of the finders. The line relays in each group have contacts corresponding to contacts (H2 and 3; connected in a chain circuit individual to the group. When subscriber 313i makes a call, a circuit is completed from ground, chain contacts 3i2, contacts 3 35, lower winding of combined line and cut-ofi" relay 3E6, contacts'32i, line 392, subscribers telephone 3M, line 393, contacts 322, upper winding of relay 3E0, middle winding of relay 3m to negative battery. Relay 3H! operates part way and closes contacts 3| 1, 3l3, 314, and opens contacts 3l2. At contacts 3H a locking circuit is closed to maintain relay 3H] energized after the operation of level start relay I44 ground on the guard lead 22? to energize the stepping magnet 252 and to deenergize relay 2%. The ground extends to the guard lead through contacts 24!, contacts 223, and contacts 25!, to cause the distributor to step as previously described. If the trouble is encountered after changeover relay 230 and relay 265 operate, relay 250 is operated through its upper winding over an obvious circuit.

During the rotary searching of the finder, should the wipers 2135 and 205 fail to. encounter battery through the subscribers cut-off relay, the shaft and wipers would be rotated to the eleventh rotary position. Upon reaching the eleventh position the cam springs H53 operate and place ground on the guard lead to advance the distributor wipers to the contacts of the next finder. Relay 2H re eases to complete the circuit of the release magnet 2% which operates to return the switch to normal.

The vertical bank contact 53'! of the tenth level is permanently grounded; therefore, if the vertical test wiper 96 has failed to find ground on the level in which the call originated, the wipers cut in on the tenth level, rotate to the eleventh position, and return to normal as dc scribed in the preceding paragraph.

The line circuits of Figure '3 may be substituted for the line circuits of Figure 1; lines 382 and 303 correspond to lines I62 and ifiliiycontrol lead 305 is connected to contact 297; and

start. lead (5 corresponds to start lead H5.

opens the initial circuit; at contacts 352 a circuit is opened to prevent the operation of line relays that are in that part of the chain further from ground; at contacts 353 negative battery is extended from the middle winding of relay 319 to contact 26'? to mark the position of the line in the bank; at contacts 3M ground is applied to a winding of level start relay Hi4 and to a winding of level marking cut-on relay I33. The finder system operates as previously de scribed and switches the calling line to the first numerical switch.

When the switching relay 29B of Figure 2 returns ground to the CN lead of Figure 3, relay 3m operates fully by the. circuit extending from ground on the CN lead, middle winding of relay 318 to negative battery. At contacts 322 and 32l the windings of relay Eli] are disconnected fromthe negative and the positive lines; at contact 316 the chain circuit is prepared for relays further along in the chain; and at contacts 3!? the energizing circuits of level start relay Md and of level marking cut-off relay I33 are opened. As previously described break contacts on the level start relays prevent other lines in the group from placing ground on lead 3i5 until relay I33 releases. 7

After the conversation is completed and while relay am is releasing, both contacts SH and SIB in the chain circuit are open for an instant. Re sistor (H8 is connected across contacts 312 to prevent the release of any succeeding linerelay that may be operated.

Having fully described one embodiment of my invention it will be understood that various changes may be made therein without departing from the spirit of my invention as set forth in the appended claims.

What is claimed is:

1. In a telephone system, a plurality of finder switches, a plurality of lines accessible to said switches and having terminals appearing in different levels of bank contacts in said switches, a vertical bank of test contacts for each of said switches, each level of lines having a common marking circuit including the vertical bank contacts for that level, a vertical wiper for each finder having access to its vertical bank, means responsive to the initiation of; a call over one of the lines of a level for connecting a marking potential to the testcontact associated with that level and for causing the operation of oneof said switches to test the contacts of its vertical bank in search of said potential, and a relay in the marking circuit operated instantly responsive to the finding of said marked contact for disconnecting said marking potential from said test contacts.

2. In a telephone system, a finder switch, a group of lines accessible thereto, said lines divided into subgroups, a vertical test wiper for the finder, a test contact for each sub-group of lines traversed by said wiper, a marking circuit for each sub-group, means controlled from a calling line in a sub-group for closing its marking circuit to mark the test contact of that subgroup and cause operation of the finder to move said wiper in search of such marking, and a relay controlled over the closed marking circuit when found for opening the marking circuits of more than one sub-group of lines to thereby prevent the marking of certain of said contacts.

3. In a telephone system, a finder switch, a plurality of lines having contacts arranged in levels accessible to said switch, a vertical test wiper for the switch operated durin the vertical movement thereof to find the level in which a calling line is located, test contacts traversed by said wiper, one for each level, a marking circuit for each line for marking the test contact of the level in which that line is located, means for moving the wiper to find a marked contact, and a relay in series with and common to more than one of said marking circuits and operated whenever the wiper finds a marked contact of one of these circuits to open the marking circuits to which it is common.

4. In a telephone system, a plurality of finder switches, a plurality of lines accessible thereto and having contacts arranged in levels in the banks thereof, a line relay for each line operated responsive to the initiation of a call thereover, said lines divided into groups including the lines of more than one level, a start relay for each group operated in response to the operation of the line relay of any line in that group to start a finder switch to find the calling line, a chain circuit including contacts of the line relays of a group for insuring the operation of only one line relay at a time, and means controlled by the operation of said start relay for opening the circuits of all unoperated line relays of that group.

'5. In a telephone system, a group of lines, a finder switch having access to said lines, a common marking contact for said group of lines in said finder switch, a marking circuit, a line relay for each line operative in response to a call from the associated line to extend a marking to said contact over said marking circuit, a start relay common to said lines, a circuit completed responsive to the operation of any one of said line relays for operating said start relay, a finder start circuit completed in response to said start relay operation for causing said finder to hunt for the group of lines, operate circuits for said line relays, contacts operated by said operated start relay for disconnecting said operate circuits to render the other line relays of the group temporarily inoperative, series relay means operated over said marking circuit in response to the finding of said contact by said switch for disconnecting said marking from said contact and for causing said switch to hunt for the particular calling line, and other relay means individual to the calling line operated when the line is found to cause release of said start relay, the start relay thereupon reconnecting said operate circuits to render the other line relays operative again to mark said common contact in response to other calls.

6. In a telephone system, a group of lines, a finder switch having access to said lines, -a line relay foreach line and contacts therefor, a start relay having an operate circuit, a marking cutoff relay having make contacts and break contacts; a marking circuit including contacts of any operated one of said line relays, said cut-off relay break contacts, and a marking contact in said switch for said group of lines; a locking circuit for said cut-off relay including said make contacts thereof and contacts of any operated line relay, one of said line relays operating in response to a call from its associated line, said line relay contacts operating in response to the operation of said line relay to operate said start relay over its said operate circuit, and to connect a poten-- tial to said marking contact over said marking circuit, operate circuits for said line relays, contacts opened by said operated start relay for disconnecting said operate circuits of said line relays to render the other line relays of the group temporarily inoperative, a finder start circuit also completed in response to the operation of said start relay to cause said switch to hunt for said potential, said marking cut-01f relay operating in response to the finding of said potential to close its said make contacts for completing said locking circuit and to open its said break contacts for disconnecting said potential from said marking contact, relay means in said switch also operating in response to the finding of said potential for causing said switch to hunt for the particular calling line, other relay means individual to the calling line operated in response to the finding of said particular calling line for disconnecting and restoring said operated line relay, said line relay contacts opening in response to such restoration to release said start relay, and said opened contacts of said start relay reclosing said line relay operate circuits in response to such release to render said other line relays again operative.

7. In a telephone system, a plurality of finder switches each having bank contacts arranged in levels and having test contacts corresponding to said levels, a vertical wiper for each switch for traversing the test contacts thereof, groups of lines, each group connected to a corresponding level of said bank contacts in each switch, a start relay, a guard relay, a marking circuit for one of said groups of lines including a winding and contacts of said guard relay and also the test contact corresponding to the level of said one line group in each switch, relay means operated responsive to the initiation of a call over any one of the lines of said one group for applying a marking potential to said marking circuit, an operate circuit completed in response to the operation of said relay means for operating said start relay, a finder start circuit completed in response to the operation of said start relay for initiating the vertical movement of an idle one of said switches to cause the vertical wiper thereof to search for said potential, said guard relay operating over said marking circuit in response to the finding of said potential by said vertical wiper, and said guard relay contacts operated in response to said operation of said guard relay to disconnect its said winding and said marking potential from said marked test contact of all of said switches.

CHARLES F. FFOLLIOTI. (References on following page) 1 1 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Stehlik Jan. 17, 1928 Lomax et a1 Oct. 23, 1928 Name 7 Date Saunders Mar. 15, 1932 Taylor et a1 June 20, 1933 Stehlik Aug. 29, 1933 Saunders Apr. 26, 1938 Baker et a1 Oct. 18, 1938 Hovland Sept. 8, 1942 

